The German DAX 30 index rose 3.3% to 5797.66, buoyed by gains for ThyssenKrupp , another German steel producer, which rose 8.1% after Salzgitter's results and ahead of its own fiscal third-quarter numbers on Friday.

Hansa took over some contracts that had been drafted between Salzgitter and Sepanir to supply the Iranians with fire-protection equipment and other technical energy-industry needs—fulfilling the orders for Petrokish instead, commercial records show.

Mr. Gieseke said Minimax had been a client of Salzgitter and Sepanir before sanctions, that the stationery was brought to the meeting by a Petrokish representative, and that Minimax didn't notice the logos.

After the sanctions were published in June 2010, Hansa began to move into the business abandoned by Sepanir's former German intermediary, Salzgitter Mannesmann International GmbH, which "ended cooperation as soon as we learned the Iranian Revolutionary Guards were involved," a Salzgitter spokesman said.